In recent years, integration of the input unit and the display unit in electronic devices has become more common in pursuit of more intuitive operation and miniaturization of the devices. Particularly in mobile electronic devices such as mobile telephones, personal digital assistants (PDAs), and notebook computers, a touch panel than can detect the position at which the screen of the device is contacted by an object for detection (such as a finger or a stylus) is often integrated into the display surface of the display device.
There are a variety of types of well known conventional touch panels such as the so-called resistive touch panels and capacitive touch panels. Among these, capacitive touch panels are used especially widely.
Capacitive touch panels detect the position at which the screen of the device is contacted by a finger or stylus by detecting the associated change in electrostatic capacitance that occurs.
In many cases, the so-called sensor electrodes that detect the position at which an object contacts the screen of the device are formed using indium tin oxide (ITO) or the like. However, in large-screen touch panel-equipped devices, the resistance of the ITO sensor electrodes increases to a point at which the detection ability of the device decreases.
Therefore, the sensor electrodes are sometimes formed using metal wires arranged in a mesh pattern (lattice pattern) in order to decrease the resistance of the sensor electrodes.
When using mesh-shaped sensor electrodes, visual interference sometimes occurs between the pixel array pattern of the display device and the mesh pattern of the sensor electrodes when the touch panel substrate and the display device are fixed together. This interference is known as the moiré effect. The moiré effect also sometimes occurs due to the positional relationship between sensor electrodes that run vertically and sensor electrodes that run horizontally. Occurrence of the moiré effect is not preferable because it can decrease the clarity of the images displayed on the display surface of the display device.
Patent Document 1 discloses a touch panel device in which occurrence of the moiré effect is reduced by overlaying a first electrode and a second electrode.
FIG. 20 is a plan view illustrating the configuration of the touch panel device disclosed in Patent Document 1, in which the first electrode and the second electrode are overlaid. The touch panel device disclosed in Patent Document 1 includes a plurality of mutually parallel first electrodes 203 and a plurality of mutually parallel second electrodes 205 that intersect with the first electrodes 203. The first electrodes 203 and the second electrodes 205 each have a diamond lattice pattern, and when the first electrodes 203 and the second electrodes 205 are overlaid, a square-shaped interference pattern occurs in directions that are rotated at angles θ and 90°−θ relative to a first direction parallel to the direction in which the terminals of each first electrode 203 are arranged or relative to a second direction parallel to the direction in which the terminals of each second electrode 205 are arranged.
This reduces occurrence of the moiré effect when the first electrodes 203 and the second electrodes 205 are overlaid in the touch panel device disclosed in Patent Document 1.